people are discouraged from having sex as often and with as many people as they want to
In most cultures I'm familiar with, this is much more true of women than of men.
I'm not aware of any culture where the norms for sexual behavior are the same for men and women (though I wouldn't be surprised if that was the case in some hunter-gatherer tribes or hippie communes). The discussion may be less abstract if we separate "norms for women" from "norms for men" - I suspect traditional sexual norms for European women are closer to traditional norms for Chinese women than traditional norms for European men ("traditional" being say "a village in 1700").
It is a cultural universal that people are discouraged from having sex as often and with as many people as they want to. Every culture I've ever heard of imposes many restrictions on sex. I've never heard of a culture that shames people for being too stingy with sex.
If we assume that culture is adaptive, this means that the human sex drive is too strong for humans in society. Why is this? As sex drive is a phenotypic feature with extraordinarily strong selective pressure, why haven't we evolved to have the proper sex drive?
One reason could be that reduced sex drive is selected for at the level of the group, while higher sex drive is selected for at the level of the individual.